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Canadian Centre on Substance Use and Addiction

Regular Cannabis Use Linked to Increased Risk of Mental Illness

Ottawa, April 25, 2019 — People who use cannabis regularly — one or more times per week over a period of months or years — could be at greater risk of developing psychosis or schizophrenia, according to a new report by the Canadian Centre on Substance Use and Addiction (CCSA). Clearing the Smoke on Cannabis: Regular Use and Mental Health reviews the current body of research about the relationship between cannabis and a number of mental health conditions.

The report finds a stronger link between regular cannabis use and risk of developing schizophrenia or psychosis when other risk factors are present, such as having a family history of schizophrenia or psychosis, starting cannabis use earlier in life and consuming cannabis high in THC content. In contrast, although there is a strong correlation between cannabis use and depressive or anxiety disorders, the risk of developing such a disorder after using cannabis regularly is low.

Additional findings of the report include:

  • People with mental health conditions, including schizophrenia, bipolar disorders, depression and anxiety disorders, and post-traumatic stress disorder, are more than twice as likely to use cannabis regularly.
  • Regular cannabis use is generally associated with more harmful rather than beneficial effects among people with mental health disorders.
  • A standardized measurement of cannabis use and larger studies are needed to understand better the relationship between cannabis and mental health.

“The complex relationship between cannabis use and mental health has gained significant attention, particularly since legalization,” says Dr. Sarah Konefal, research and policy analyst at CCSA. “The current evidence suggests that there is a strong association between the regular use of cannabis and several mental health conditions, particularly psychosis and schizophrenia. However, this does not mean that one causes the other and numerous factors contribute to the development of mental illness.”

“Most individuals who use cannabis do not go on to develop mental health conditions and most people who experience mental illness do not necessarily use cannabis. Further research and standardized measurement of cannabis use are required to establish a better understanding of this relationship.”

This report is the latest in CCSA’s Clearing the Smoke series on cannabis. The series looks at how cannabis use affects the mental and physical health of Canadians. Additional reports in the series address cannabis and cognitive function, cannabis and driving, and cannabis use during pregnancy.

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